The invention relates to laminated materials comprising a substrate having metallic suspension coatings, and more particularly to materials of this type as used for the production of plain bearing elements.
A prior method for the production of laminated materials as known by German Offenlegungsschrift No. 19 23 030 provides for the preheating of a cleaned, roughened steel base strip. Then an intermediate NiAl layer is applied, whereupon AlSn wire in the form of a melting compound is fused and sprayed on, the sprayed surface being rolled and the composite article subjected to a heat treatment for about 1 hour at 300.degree. to 350.degree..
However, the above described method for the production of laminated materials using highly adhesive intermediate layers comprising molybdenum and nickel aluminide has the disadvantage that it cannot be subjected to concentrated loads, impact, milling or rolling operations because of the likelihood of separation of the coating from the substrate, making the parts useless.
The German Disclosure reference No. DT-OS No. 23 60 523 describes a method for the production of a laminated material by spraying a metal layer onto a substrate of aluminum or an aluminum alloy. The oxide film on the substrate surface is counteracted by an adequate adhesion to the sprayed-on metal coating, but this has the effect that the sprayed-on metal layer tends to peel off. To avoid this disadvantage it is suggested in the disclosure to spray on a thin intermediate layer of a highly adhesive material such as NiAl or Mo.
The disadvantage of this method as set forth immediately above is that the materials which are sprayed on, are applied over the oxide film of the substrate material, and therefore the bond is likewise not sufficient to withstand the above mentioned loads.
The German Disclosure reference No. DT-OS No. 23 60 523 also describes a method to eliminate the automatically or ever-present oxide film of the substrate material. Zinc is substituted in or precipitated on the surface, and the desired materials are then sprayed in layers onto this zinc coating.
Due to the time-consuming and difficult nature of this pretreatment, the method which it utilizes does not represent an economical solution for the production of laminated bearing materials either, because it is applicable only to parts which undergo no further deformation, and is not suited for a continuous manufacturing operation.
German Auslegeschrift (Provisional Patent) No. 2,130,421 describes a method for the production of laminate material by dropping a molten mixture of aluminum and lead onto the surface of a substrate strip. Such dropping may be free falling down, or may be accelerated by downwardly directed streams of inert gases.
For better adhesion between a steel base and a coating alloy, the German Provisional Pat. No. 2,130,421 proposes to apply, prior to the actual spraying, either by immersion in aluminum or in an aluminum alloy, or else by the application of a suitable powder, or by spraying-on a very thin Al film, a metal coating which is compatible with the actual, later-applied coating alloy and which does not form a thick, brittle intermediate layer with the steel.
German Disclosure reference No. DT-OS 17 75 322 explains a method for the production of laminated steel AlPb material for the manufacture of plain bearings. In this known method, initially a so-called "green strip" is produced as a semi-product by rolling together a middle stream of AlPb powder and outer streams of aluminum powder to form a strip of three layers of different composition. Thereafter, this "green strip" is plated onto one surface of a substrate strip by rolling. The disadvantage of this method is that due to the inevitable intermixing which occurs when the layered powder is running into the rolling gap, the three layers are not distinctly separated. Due to the subsequent sintering and rolling operation required in this method, uncontrollable diffusion processes take place on the one hand which lead to the formation of brittle phases that impair the bond. On the other hand, due to severe deformation, the somewhat round Pb particles become elongated with the result that failures of plain bearing elements made of such laminated materials will occur because of the internal notch effect as the Pb fibers are stressed to the endurance limit.
The fact that all such prior coatings still have quite substantial deficiencies is known ["Jahrbuch der Oberflaechentechnik" (Yearbook of Surface Engineering) 1956, pages 261/306]. The significant disadvantage thus is that, in addition to the necessity for producing intermediate layers for a better bond, an additional thermal after-treatment must be carried out, and that in spite of this the coating still will peel off or partly chip off, when producing the workpieces. It is believed that this peeling or chipping can be attributed in part to the formation of brittle, inter-metallic phases.
In view of this, it is an object of the present invention to provide an improved laminated material comprising a substrate and a coating of metallic suspension alloy, that is characterized by a high bonding strength and also good deformability, so as to make it possible to produce, from such laminated material, various workpieces and in particular plain bearing elements, without additional thermal treatment such as sintering. Moreover, the invention has for another object the provision of favorable production methods for the manufacture of such laminated materials.
According to the invention there is provided, in order to solve this problem, a method and product characterized by a coating that starts as an alloy which has a tendency to dissociate whereby upon cooling from the molten state it becomes a suspension or mixture (often referred to as a "suspension alloy"). This coating substance or alloy is applied thermokinetically to a substrate as a molten alloy that tends to dissociate, and upon its solidification the components dissociate and become chemically separate. The coating is then compressed together with the substrate; in accordance with the invention the substrate surface that receives the suspension alloy is in the form of either a rough base, or else an aluminum or aluminum alloy surface characterized by a surface activation and grain structure (de-oxidization) that is produced by brief heating to a temperature between 450.degree. C. and the melting point of the aluminum or aluminum alloy, this being preferably accomplished by the thermokinetic coating procedure.